Airport lighting system



`Fuly 8, 1952 H. A. CLINE 2,602,350

AIRPORT LIGHTING SYSTEM Filed May 25, 194e 5 sheets-sheet 1 'IN VEN TOR.

ATTORNEYS ABY July 8, 1952 H A, CUN; 2,602,850

AIRPORT LIGHTING SYSTEM Filed May 23, 1946 5 Sheets-sheet 2 :HIS-2 INVENTOR.

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ATTORNEYS July 8, 1952 H. A. CLINE 2,602,850

AIRPORT LIGHTING' SYSTEM Filed May 23, 1946 l 5 Sheets-Sheet I5 -gs I 36* 8a y A A l y gm gw gm gmgmfgn gm gm mm IJ/z l /l3 f (14325 `/85l @"7 l /03 35 /o2, 82 ./0/ INVENTOR.

ATTOBNE YS July 8, 1952 H. A. CLINE v AIRPORT LIGHTING SYSTEMv 5 Sheets-Sheet 4 Filed May 25, i946 JNVENTOR. MQ. @brei/75 ATT ORNEY `July 8, 1952 H. A. CLINE AIRPORT LIGHTING SYSTEM Filed May 23, 1946 5 Sheets-Sheet 5 Fifi-13 /eo uuu-"Hur @-115- /5 7 me uhm, Il /58 [67 lillll IGZ ISL.

ATTORNEYS INVENTOR Patented July 8, 1952 AIRPORT LIGHTING SYSTEM Harold A. Cline, Dayton, Chio, assignor, by rnesne assignments, to Emarco Corporation, Chicago, Ill., a corporation of Illinois Application May 23, 1946, serial No. 671,696

In the operation of aircraft, it isyof primary importance to provide a reliable system by means of which the pilot can be assured of making a safe landing of theaircraft, especially under conditions which approach the limiting conditions of visibility and ceiling.

Variousv blind landing systems are known by the use of which it is-possible to land an aircraft.

without visual contact with theground, such systems require both special training and special equipment, as well as a high degree ofaccuracy and reliability in the instrumentation used. An error of only a few feet inthe measurement of altitude, for example, can result in landing conditions which vary from merely unpleasant to actually dangerous, both to personnel andtothe equipment involved.

The visibility of the landing field can be im# proved materially, both for daylight flying and particularly for night operations, by the use of properly constructed andV arranged 'lights for outlining the yglide path and the actual landing strip. The use of a high intensity beam directed toward the approaching aircraft has not proven to be highly successful and may even create a serious night hazard. Where visibility is good, the high intensity beam may have a blinding elfect which adds to the pilots diiiic'ulties in bringing the aircraft to a proper landing.` `If directed along the line of flight, the high 'intensity beam has been found to create an illusionof height, such that the pilot is apt to level the ship for a landing while. still well above the ground level. Under adverse Aweather conditions the usual high intensity beam is found Vto have low penetrating power .and isfeither absorbed in a relatively short distance, or may appear merely as a blur of light without properly identifying a position or location. 1

It is accordingly the principal object of this invention to provide a landing' iield lighting system whichdevelops a large amount of light of such character -that it is highlypenetrative of fog, mist, and the'like, andyet which is not blinding anddoes not interfere with the continuing vision of the pilot at any lstage ofthe final landing operation. v g l -1 M 'i It is also anobject to provide a series of lighting vunits particularly adapted for identifying vthe glide path in advance ofta landing field, each of the units being in the form of a blanket'ofsubstantial area. v

-It is also an object to provide a'lightin'g system of such character in which-the -quantityfof :light developed by each ofthe individual units inaybe readily controlled` while maintaining substantially uniform light intensity over a substantial area of the light source.l f j f It is alsoan vobject to jprovde an improved airport lighting system which includes selectively 6 Claims. (Cl. 177-352) operable light sources havingidenite vcharacter'- istics as to colorand arrangement for identifying the proper 'runway for landing and l`other selectivelyV operable light sources locatedV outwardly of the runway and of contrastingly different characteristics as to color or arrangement for indicating the glide path.'

yt is a further object to provide a lighting vunit inthe form of a blanket havingal substantial area capable of being' readily identied ,and in which the light is distributed over a substantial angle transversely ofpthe normal direction of'` flight tov provideV for proper viewing Ithereof" by the pilot notwithstanding his /position'to oneside or the other ofthe unit.

Other objects and advantages .of .the invention will be apparent from the following description, the accompanying drawings and the appended In the drawings, which illustrate 'a preferred embodiment of the invention- Fig. 1 is a schematic view illustrating an airport provided with a lighting system in accordance with the present invention; f

Fig. 2 is a to'p planr View of one of the lighting units utilize'd'for defining theappi'oach or glide path in the lighting system of the invention, with the central'portion thereof being broken away in a plurality of layers toillustrate internal construction; 'v H Fig. 3 is a View in end elevation of the lighting unit shown in Fig 2; l Y

. Fig. viis anenlarged partial section taken substantially on the line 4-4 of Fig;,2;,

Fig. 5 is an enlarged partial section taken substantially on the line 5 -5 of Fig. `2;

Fig. 6 is an enlarged'v partial section taken substantially on theline 6-'6 ofLFig. 3;

Fig. 7 is a wiring diagram lfor the lighting unit showninFigZ; f 'D ing. 8 is a diagram of a modined for'm of ecn,- trol Icircuit for the unit; Y v

Fig. 9 is/-a viewinside elevation, partly in vertical section substantially on the line 9-'9 in Fig. 10, illustrating `*one of :the lighting -units :utilized along the airport runways in the lighting: system of the present invention; f 1

Fig. 10 is a top planrview ofthe lighting unit illustrated in Fig; 9; l

Fig. 11 is a view in vertical section .taken'substantially on'the line II-Ii in Fig,l 9; Fig. 12 is a"wiringdiagram for the lighting sys-'- tenishowninl'igs.Q'to11;` i

Fig. 13 isa broken' side elevational viewof a unit adapted for marking the endofa" runway orofthefield;` ff

Fig.A 14 isa view partially" in end'elevationand iiirtially in vertical 'section online'H-Hl of Fig.

Fig. is a wiring diagram of the unit shown in Figs. 13 and 14 Fig. 16 is a polar diagram of the pattern `of light distribution from one of the approach units; and

Fig. 17 is a diagram illustrating the manner of arranging the lighting units on the glide path.

The airport illustrated in Fig. 1 is shown as including an administration building Y2|), Va control tower 2| and a plurality of runways arranged to provide for landing under a variety of wind directions, i. e., an east-west runway 22, a north-south runway 23, a north east-south west runway 24, and a north west-south east run-way 25. Each of these runways is shown as provided along its .outer edges with a plurality of light sources L26 substantially outlining the runway. These light ysources are preferably arranged in a definite pattern .as to location and color ,characteristics so that they will `lie-readily identifiable by the ypilot andY so that he can determine `accurately the location of the particular runway on which he is ,to land. ,Preferably as vindicated these light sources are ,arranged in a double line located substantially at :the outer boundaries of each runway.

A plurality of other light sources 21 are `arranged adjacent the outer ends of each runway to designate the glide Apaths thereto, and these lights are arranged in a contrasting pattern so that `the glide path will be clearly marked as separate and distinct from `the runway. Preferably the glide path light sources 21 are arranged in a single line which continues in the same direction as the glide path Iand which may be either colinear with the center of the runway, or as shown, oiset toward the left of the runway sumciently to facilitate the viewing of a series thereof by the pilot, who is usually located at the left of the center of the plane and whose direct forward and downward vision is sometimes hampered by the fuselage of the plane.

Figs. 2 to rI illustrate a lighting unit found highly satisfactory lfor use as light sources 21 in the lighting system of this invention. The housf ing for the lighting unit is shown as a rectangular, boxlike structure formed of side panels of steel, aluminum or other suitable materials and a bottom panel 4| secured together as by welding to a plurality of angles -42 and 43. Three heavier panels 44 are shown Aas secured in Ysuperimposed relation on bottom panel 4| across the middle and each end of the box, and the outside of each of'slde panels 40 is similarly reinforced by means of panels 45. The bottom of the box is shown as furtherreinforced by means of channel members 46 arranged to extend'diagonally between opposite corners at the bottom of the box and firmly secured as by welding to the bottom -panel 4|. These channelsrare in turn welded to a bearing plate 41, which is preferably square and has va stud bolt 48 permanently secured thereto, as by means of the welded joint indicated at 43. This stud bolt 48 is in turn jour-y naled in a supporting plate 50 and secured vby means'of nut 5| and lock washer 52.

Plate 50 is preferably round and has two bracket arms 5.3 welded or otherwise rigidly secured thereto and extending perpendicularly downwardly therefrom. Armv members 53 are provided with opposing holes adapted to receive a pin or shaft 54 which is in turn supported in similarly opposing holes in the upwardly extending arm portions 55 ofy a 'U -shaped bracket 56 and is provided with threaded ends adapted to re- 4 ceive suitable nuts 51 and lock washers 58. Bracket 5S is adapted for permanent mounting, :as v.by means of :bolts or rivets engaging in holes .55 and set in a `suitably permanent base such as concrete. In such mounting in a system of the type shown in Fig, 1, bracket 56 will be so positioned that shaft 54 will be substantially transverse to the line of the glide path, so that the entire unitmay be tilted in the plane of the glide pathzto .control the A,direction of projection of the 'light emanating therefrom and may be locked in the desired angular setting by means of nuts 51 and Washers 58. At the same time, bolt 48 and itsnutand washer provide for adjustment of the unit on an axis at right angles to shaft 54 and similar locking in adjusted position.

The top for the .housing shown in Figs. 2 to 5 is formed of 4four vangle irons 6D having'their ends mitered and welded together. A smaller angle 6| is welded'orotherwise secured to the inner surface of each angleV 60.in such manner as to provide Aa channel adapted to receive the edges of `a glass plate '62, which issecurely held within the channel by vsuitable packing or sealing means (i3-such as a rubber gasket or a suitable plastic. The angle 60 along one side of the housing-top is shown as secured through hinge 64 to its adjacent angle `42 on the body of the housing, and a plurality of lock elements are also shown as comprisingpairs of short, rightangled tabs 65 and 66 welded or otherwise secured to angles 42 and 60 and adapted to be drawn together by means such as bolts 61 and wing nuts andwashers 68. When the top of the frame is closed, the inner flanges of angles 42 and 60 are adapted to engage in abutting relation, and the whole'may be firmly secured by a suitable fastening such as wing nuts 68. This provides a substantially weather-tight enclosure for the lighting elements themselves while at the same time permitting ready access thereto for 1sfirvicing, exchanging burned out tubes and the 'I'he mounting means for the gaseous discharge tubes 35 is shown in detail in Figs. 3, 4 and 5. As shown-each of bottom panels 44 of the housing has secured thereto as by welding an angle 10 extending across the housing. To each of these angles 10 there is secured a panel 1| of rigid insulating Amaterial such for example as Bakelite. Panels 1| are-'shownV as secured to angles 10.by means offbolts'tand nuts 12, and along the upper edgeof each of panels 1| there is secured as by means of rivets 13 a further angle 14. Bolts 12 and rivets' 13 also serve to secure to the' other side of the two end panels 1| three bracket members 15, shown asv composed of a pair of strips of angle iron having their adjacent corners "mitered` andwelded together to form` a right angled joint. The brackets 15 along one end of the housing serve to support a strip 16 of copper or other conducting material which serves as a common-connection to one end of each of tubes 35, such connection being grounded to the frame as indicated at 11. As shown, these tubes are' secured to strip 16 by means of a plurality of clip members 18, each of which is adapted to receive and hold an end of one o1' said tubesand one of which includes a projecting bolt 19 which extends through strip 16 and is held in electrical contact therewith by means of nut 80.

The construction at the opposite end of the housing from strip 16 is substantially the same with the exception that the corresponding strip .g5 8l is composed of non-conductingmaterial such as Bakelite or the like. A'choke coilv 82 or equivalent reactor device is connected with the' end of each of tubes 35 opposite copper strip 'lvby means of a wire 83 leading to the appropriate 'clip 18 for each of respective tubes.I Although Fig. 2 shows only a single coil 82 itwill be understood that a similar coil is provided foreach of tubes Each tube is also provided'with a reflector 85 formed from aluminum orfothersuitable material. As shown particularly` in-'Fign 4 each reflector 85 has the general 'formation' of. a trough open at the ends and is curvedlin the plane perpendicular to its length-or axisl Each of reflectors 85 is provided along its side edges with a downwardly depending iiange portion 86, and each of Bakelite panels 1I has its upper edge scalloped or similarly cut out at 81 to provide a groove adapted to receive the curvedportons of the reflectors and is also provided with a plurality of slots 88 for receiving flangesv 86 onv reflectors 85. The reflectors 85 are secured in place on angles 14 by means of screws 89. This provides simple and accurate means for properly positioning the reflectors in the frame, and providing for ready removal thereof for cleaning and the like, assuring the replacement thereof'in the n same accurate relation to the lights'ourc'es.

In assembling the unit each of "thetubes 35 is mounted within'its vrespective reflector and generally parallel withy the length thereof, accurate positioning of the tubesf being readily obtained by suitable adjustment fof clips 18 and their supporting bolt portions 19.` Where parabolically curved reflectors are used, the tube may be located substantially at the principal focus of the reflector, thus providing for directing the maximum light intensityv in rdirection substantially normal to the plane of the nit. However the reflector also provides forzdirectingia substantial'amount of light throughw'a relatively wide angle transversely of the length ofthe tubes, such angle being substantially'greater than 90 and preferably approaching-about 150. This assures that a pilot approaching the'light from one side or the other will bein position to observe clearly and to receive a substantial amount of light therefrom, the pilot thus being readily able to orient himself and establish" the-proper relationship with regard to'thevg'lidefpath and the runway r Further, since the -tube hasr substantial axial extent, it provides for Vdirectlnglight over an even greater angle in the direction'of the length of the tubes, i. e., in the normal direction of flight of the aircraft thereover.v Thus `the pilot can readily observe the light source from a remote position and at a relatively flat angle,l even though the plane of the unitmay be substantially horitime assuring that'the intensity at any point will not be so great as to be blinding. Thus the maximum intensity' in the direct line of focus of the unit is within such value' as to preclude a blinding l condition, and-the pilot l.can continuously observe y the unit as the plane approaches and passes over the same, vwithout objectionable effects or otherwise impairing his perceptionv of vision in completing the landing operation. j y

The gaseous discharge tubes preferably are of the type containing inert gases such as neon, krypton or the like,r and preferably are constructed to carry normal energizing currents substantially in eXcessof those customary with the neon lights as u sed in'` signs, etc. In the'latter case a discharge'currentfof the'order ofl .015 to about .060 amperefis commonly used, but it has been found that improved` resultsV are obtained with a greater light intensity where this current isincreased up to severalhundred milliamperes, varying up to 1/2 an ampere or more. While the increase in the total light developed is not directly proportional to the increase in current, the use of these higher current 4values has been found to be highly advantageous as providing forga solid column of light of the controlled high but nonblinding intensity. A suitable ,electrode construction for use in suchtubes is shown in Patent Nol 2,061,390,` the tubesI themselves being preferably formed of heatv resisting glass such as quartz. Pyrex, lead-glass or the like fto provide the desired strength vand heat resistance'` f The selectionv'f thegasgis ofsubstantial importance as providing furthe development of light f of the proper Wave lengtl'VVV to have the desired therefore, makeuse 4of, neon gas with 'or without the use of other gase'sand `are such as vto develop initially substantially the greater `part of their light energy "within vthe'ruige of f above 5800 angstrom unitsand preferably within the range of 6300 to angstrom units; Where a light of green color is desired, such 'for example as for marking the boundariesbf the field, or the'like, a tube containingy mercury vaporl and operating Y in the increased current range above indicated may be employed, providing for development of a high efficiency source 'ofgreen light. However because of the greater absorption of the shorter wave length of. green light by mist or fog, the source of red light is preferred for'the approach or glide path/identifying units 21 asherein described.

In some cases it has been found desirable to arrange the reflectors vso that different tubes of the unit will project thelight with a somewhat different distribution pattern.: "For example, the reflector associated withV the central tube or tubes may have the greatest depth and provide the maximum focusing effect normal to the plane of the unit. The reflectors of adjacent tubes located laterally of suchY central tube may then be of progressively different characteristics providing a wider angle of distribution, with the maximum angle of distribution taking place from the :laterally outermost tubes; This arrangement further assures thedesiredcontrolled high intensity when the aircraft in.-thenormal position but provides adequate-light throughout-the entire range of angles.toJacilitate-.observation whenthe ...pilot is.somewhat.oflthenormallcoursa'.

. lFig. 'Isliows a,typcalcircuitarrangementffor the control bf'theeirciiitsLto Vone oftheunits. As

there shown the.power..sourcev is indicated at.

|00,V supplying power ,tov a: suitableV switch |0|.

.One side` of thelightis .connected toa common bus |02 Vfromwhich connectionlis made `to the reactors 82. "lhe reactors inturnare connected .to oneend ofthe tube. with Iwhich they are associatedfthefopposite. ends of-,the tubes being connected through.Y a. common. .busl |03 to ground, .and also totheoppositeside'ofA the switch. The closing of. switch .|0| will .therefore Aresult in the simultaneous kenergiaation of Vall the tubes ofthe particular unit. Switch. .|0I .may be located in the airport controlftower, and may be arranged -ffor.operation.. concurrently -withv .the similar switches lof. all of` .thennits associated with a 1 particularglidepath so. that ,the enti-reV glide the. total quantity.. of light-developed Yby the unit, while rdeveloping substantially the same intensity oflight, over UVeachcunit ofarea of the source. Such a control may be desirable for exampleto vary thel lgihtv output depending upon the weather-conditions,-a relatively lesser `light output suilicing under favorable visibility than when visibility v is poor.

For. this purposeacontrol switch ||0 is provided which has an elongated sector I II movable into successive contact with a series of switch points. Point ||2 yis connected to the central reactor2` and'through it to the central light source 35. YWhen the sector moves into contact with rswitch `point ||2 only the central tube will be energized; and will develop light at thesame controlled intensity, but since the area producing -the-light-is-greatly reduced, it will be evident that thetotal light developed will also be substantially lower. `Where lthe vunit comprises eleven tubes, this condition will result in developing only one eleventh of the total light but the intensity' over the -lighted area'will remain the same. Under; good visibility conditions this will give a clearly visiblelight andadequately `enable the pilot to ascertain his position and land the ship safely,y Withthe use of only one tube out of -theunlt effecting a corresponding saving in power. i'

. .Under less favorable.visibility conditions sector is moved furtherHto-bring it'into contact with switch point ||3. As .shown this provides for thel energizing oftwoadditional tubes, giving a total-of three such tubeswhich are energized and a corresponding increase in total light developed. Y

IWhenlf'rnoved into: contactwith switch point ||4,'additional tubes on'each side are energized,

' giving a total of seven tubes and a corresponding lincrease in'fthe .lighted area and the resulting :form intensity overH the lighted area. This provvides a light sourcefofflargeftotal light capacity, i' readily fvisible to-ithe'pilotirom practically any'` angle 'of; approach; .fof controlled non-blinding f intensity and.o'such' distinctive'gcharacteristics as, to color; -sizev and-shape; that it is readily identied: either was'l a lsingle [unit or; when-- Varranged irrafseries deflningfthe glidepath.

1A suitableiunit has been' found; to -be'one having eleven parallel; gaseous ydischarge tubesv each having aflengthiot'aboutfourA feet and so yarranged as to form a light source approximately 'fourifeet on aside. 'The-light distribution pat- --tern is jtypicallyffshown.in'ligr16 where the observed light intensities arel-shownrby *curve* H6 l for the plane parallel Ltofthe-tubesandpassing through-.fthecenterofthe Vassembly and-bycurve I for:thefplaneperpendicularto the tubes and passing-:through the center Tofv the assembly. .As

' shown, the'halffpower points-H8 onfcurve I I6,

i.- e.; the gpointsfwhere" the fradi' are '.707 times the' maximum* radius,l deiineranr 'angle of' about 118", while `:for curve the-half `power npoints I I9 f deilne'l anv angle-of about 35. It will vthus be evidentthat thelight source I'willhave high yvisibility over aboard'range of angles the direction parallel torthe tubes, i. e.; the normal direc- 4tion cf-iight of the aircraft over the'unit; and vwill alsohave substantial visibility `in theplane at right ang-les thereto so4 that1even-ifzthe aircraft is laterallyr off-y course,v 'the light will'still be readily visibler` i a Figs;- 9,-to 112 illustratefarunwayilighting unit which has been .found Asuitable' `fornsex-in the lightingY systemvshown'in*'Fig.-fl. f InFigs. 9 to 11 the housing for 'the light isY shownas comprising,y ai Vgenerally `rectangular box 20 formed from suitable.'- sheet 'metal' -and-provided' along its upper edgewitha. iianged-construction which includesan annular.` shoulder "l 2 |r andi an' outwardly projecting-flangeportion |22. "Shoulder I2 I serves to supportthe edges of 'the periphery ofy a yglassy cover 7| 23 which fis-'secured'therein by sealing meansw|2||such as a rubber lgasket or a suitable plastic` material vThis f ylight 'unit `is equally well' adapted for. mounting along an airvport runwaymr infl the *runway 'itself andfilush with' lthe surfacethereofffindicated'` at' |25, in which -casegflass cover|23-should-be 'made of suitable `tempered glass ofastrength' sufficient vto support anfairplane passing 'thereover 'along therunway. :Flange :|22provides' a/ convenient support.- for.- thefzhousing iand may' rest' on any suitable Asupportingfmeanssuch as' a Ycradle of wood, cement or other material.

Withinv housing |20 there yis mounted one, or preferably a. plurality of gaseous 'discharge tubes. Wherea pair of tubes'are used they may bevof contrasting colors suchasafgree'n tube |30 4and arred rtube 13|. 'These/tubes arefshown as supported at their;A ends4 by clips I 33 similar to fclips 18 ,inFigsf 2 to 6. 'Clips I 33 are shown as supported by blocks |34 'ofwood at `each lend of the housing, and additional support for the tubes may be provided-by' suitable wooden supporting "strips |35 spacedwithin'the' housing and supported. Itherein'inianyA suitable way such as by means'ofscrews |36 connecting the ends of the strips with.1thesides o1' the housing.

:The wiring arrangement forthey light unit v.'shpwnir'iFigs.Av 9 to V12'is diierent from that in the othersunits since itfis': desirable to be able to energizeseleetively iither' of the tubes without LablyWvithinthe-control ltowenwhich maybe op- "eratedrto closefacircuit through' either' 'of tubes -Isnandf |3I.:It1wi111a1so'be understood that au bolts |53V for *supporting the tube brackets`|54 whichilare mounted adjacent either end of the unit.1 Tubes |55 of the character described above are mounted in such clips ateither side of the support..'.;.

A supporting assemblyv is .also provided at either end ofthe casingand islnotchedV as shown at |58 Ato receive reflectors |50 therein; A sheet metal casing IGU havingapertured sidewalls |62 and an openbottomis ,removably vreceived over the base |50. The casing includes end Walls |64 suitably secured aspbywelding the turned' over flanges |53 ofthe sidewalls thereto. AClips |65 provide for detachably securing the housingin assembled position lon the base. g 1

The apertures in the-.side walljopposite ,the tubes |55 are enclosedby glass' plates |65 which are held in position by flanges |61, the plates being suitably secured thereto with water-proofing material so-thattheentire assembly is weath- If desired the tubes rongQDposite sides of the unit may be-ofv the same color or one may develop a red lightrand the other a green light. In the latter case the unit may advantageously be placed so that the green lightappears to the pilot coming into the runway, andv so that he will have a definite marker forthe end of the runway and know that having passed rsuch light the plane can be safely landedQAtvleast one and preferably a plurality of such units are located in a line extending across the end of the runway. On leaving either end of the runway, only the red light would be observed and the pilot would thus be warned of the exact location where it was necessary to get the plane off the runway. With the construction shown it is not possible to see both lights at once and the pilot sees either a red or green depending upon whether he is leaving or approaching the runway. Y

It is found advantageous to provide for energizing such dual light source from a common transformer and with the two tubes in series relation with each other as indicated in the wiring diagram of Fig. 15. The primary of the transformer is indicated at having taps for being energized from different primary voltages and also having a tap at a somewhat higher voltage for the connection of a condenser which can be used to improve the powerfactor of the-circuit. The secondary of the Vtransformer is shown at |12, and may develop approximately 1600 volts to beapplied to the two tubesA invseries'for vthe energization thereof. While this-:voltage 'is' available at the time of startingfthe characteristics of the transformer are preferably such that when the tubes have oncebeen placed in operation, with a current flowing therethrough, the secondary voltage will be suitably reduced to provide a desired current iiow. y

In the operation of the system shown herein, the operator in the control 'tower will select a particular runway on which it is desired to have the incoming plane land, as determined by pre'- vailing wind conditions. Assuming such runway to be the northwest runway, i. e.;.runway `725 as shown in Fig. 1 ,fthe runway/lights 2.6; identifying and marking the"sidezboundaries` of` that runway will be energized bypclc'sing .the circuits to these particular lights. `thus producing' marking lights along the side edges ofthe selected runway either in red or greenasdesired.' At thesame time the unit or units |50 A'across the approach end ofthe selected runway `are also-energized, vshowingvgreen toward the incoming; aircraft.u Likewise the seriesv ofV approach lights :2l: associated with the selected runway are energized. The usual wind tetrahedron or direction; indicator may also be outlinedby a seriesgof the elongated gaseous discharge ytube lights; of this invention and this also supplements -the other landing equipment in showing the proper direction for landing.

Approach lights 21 extend well in advance of the actual runway, the distance in any installation being determined in some measure with relation to the glide angle and the minimum permissible ceiling'conditions. Where for example the glide angle is 21/2" it is advantageous to have'such lights Vextend beyond the end 'of the runwayfor approximatelyl50`0 to 2000 feet, vor farther, to enable the pilot'to Iidentify suchseries of lights even under poor. .visibility'conditiorlsfA well ahead of his actualarrival over the runway." i

While the' longitudinal'spacing'of the lighting units 21 may vary, it is preferrd'thatthey be arranged with a uniform spacing to better enable the pilot to orienthis position,` a suitable vspacing being of the order of 50 to 100' feet. In ,this way the pilot is enabled to identify' a series'of such lights, and to be lcertain that they are landing field lights as distinguished fr'm'roadside stands, or other general purpose lights.' Further; if desired, and particularly where the groundslopes sharply in advance of the runway. the lights may be mounted above the ground'level and so as to present a substantiallyuniform 'appearance and depth when viewed from the approaching plane. The ability to view a number of such lights in va regular and uniform pattern is highly'desirable as giving a line of positioma condition'which is not obtainable wherethe pilot jcan"`seel`only one vlight at a time.'

Referring to Fig. 17, the series of vlights are indicated diagrammatically in*k reference" 'to the glide path and an arrangement is shown inwhich the angle of the unit relative to the ground level varies progressively solas to develop maximum visibility for the pilot. j Thusjtheangle a between thepperpendicular |8| andfthe planej|82 of the surface of the unit 21 at the outer` end of the series of approach lightsmay be. relatively large, approaching so that the maximum'vsibility will be available Whenthe pilot looks downward. As the runway is approached, this angle becomes less and at the finaljpositionlthe angle may be reduced to 15 or 'even less "soi th'a't'the unit is substantially'` normal tothe' glide path.

As a pilot comes in on a glidep'ath'; Qh' should be able to identify one or more offthe'lighting units before 4he dropsbelow; thel minimumaltitude level. Having identifled-'the'units" because of their large size and distinguishing characteristics, as well'asf-theirclos Yarrangementin a series, the pilot. can thencontinue ontlie ,glide path even though fullvisibilitylofothe; land iobjects may be obscured- Even inthe Vfinal landing operation and at the closest approach to the light sources there is no objectionable effect and the pilot can continue to look directly at the lights which. at all times afford an accurate indication of. the ground level 'without distortion or optical illusion, completingv the landing in this way with vreliability `and confidence. The presence ofthe marker'lights at the end and along the runway further. indicates the final position infront of the administration building to which the ship is to be brought.

l While the'forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood' that the invention is not limited tothese precise forms of apparatus, and that changes may be made therein without departing fromthe 'scope of the invention Vwhich is defined in the appended claims.

What is claimed is:` l

1.1I-n an airport lighting system, a series of light sources arranged in a single line for marking the glide path f va landingl field inV advance of therunway, each said source comprising a plurality of elongated? gaseousV discharge tubes of predetermined,non-blinding intensity mounted in general parallelrelationto'each other to thereby aflord'a blanket -lightsource of relatively large surface area, and elongated reflectors mounted around said tubes andsubstantiallyparallel to saidegude path for distraining the light from said tubes in a wideanglej transversely of said flight path to provide for vvisibility thereof from an aircraft approachingat a substantial angle to either side Of the'nerfmal iliehtpath, there being a` plurality of otherlightjsources arranged in a double line along said runway and having like characteristics "substantially definite and readily distinguishable from said .glide path light sources.

2. In an lairport lightir'ig' system, a series of light sources arranged asirigle'y line for marking the glide path of a landing fleld in advance of the runway. each said sourcecomprising a plurality of, elongated gaseous 'discharge tubes mounted lin general parallel relation and adapted to be positionedrin generals alignment with the normal'path of flightbfan'aircraft thereover in landing toA thereby afford a 'blanket' light source of relatively large surface area, and elongated trough-shaped reflectors :mounted 'around' Ysaid tubes and opening toward said normal ,path of flight for distributing the light fromY said tubes in a wide inglel transverselyfsaid flightv path to provide for,l visibilityf offsaid light from an aircraft app'roachingat'a substantial angle to either side of' the normal' flight" path," 'the` central 'ones of said plurality of 'tubsbeiiig'rnounted deeper in said reflectors 'than'the terl ones'thereof to thereb'yce'ct increasedA light intensity'icentrally ofsaid angle.

3. An'ai'port lighting system comprising, in combination," ia plurality of light sources arranged in a" single line extending beyond the outer end of arunway' of the airport for asubstantial distance to' deilne agli'clepath, each of saidlight sources being in the'form' of va blanket of substantial area, and 'a' plurality/fofv other light sources arrangedin' a doublelnealongr said runway and` having light characteristics substantially different andY readily distinguishable from said glide path light sources.

4.` An airport lighting lsystem comprising, in combination, a plurality Vof light. sources arranged in 'a single line extending beyond the outer end of a runway of the airport for a substantial distance to define` a glide path, each of said light sources comprisinga plurality of elongated gaseous discharge tubes arranged side by sideVV forming a blanket of substantial area, and a plurality of gaseous discharge tubes of different color characteristics from said glide path light sources and arranged in a double line along said runway.

5. A landing field lightl comprising a base, a plurality of elongated gaseous discharge tubes supported on said base in a row and in substantially parallel relation to each other, a plurality of reflectors mounted on saidbase for reflecting light from said tubes outwardly away from said base, each of said reflectors being disposed between said base and arespe'ctlve. one of said tubes, said Vtubes and said reflectors being disposed on said base in position wherein when adj acent' tubes are energized the light therefrom is directed from a substantially continuousarea of said base and is of an intensity substantially equal to the light directed from said base when one of said tubes is energized, and means 'including4 a switch connected to said tubes for selectively controlling the energization of adjacent tubes progressively along said row to thereby vary the 'said area of light and thereby vary the quantity of light directed away from said base.

6. A landing field lightcomprising, a box hav-V ing one transparent side, a plurality of gaseous discharge tubes mounted in said box in a row in substantially parallel relation to each other, said tubes being of the character effective to carry discharge currents of more than .060 ampere and less than .500 ampere, and reflectors mounted in said box on the opposite side of said tubes from said transparent side for directing light from said tubes in a substantially continuous sheet outwardly through said transparent side, said reflectors being soY disposedV in said box that the 'intensity ofthe light directed outwardly through any unit area of said transparent side is substantially equal to the intensity of the light directed outwardly through any other equal unit area of said transparent side.

' HAROLD A, CLINE.

REFERENCES.- CITED The following references are of record in the le of this patenti UNITED STATES PATENTS Number Name. Date 973,685 Moore Oct. 25, 1910 1,540,123 Hartneyv June 2, 1925 1,656,163 Gatkowski Feb. 7, 1928 1,706,091 Wiegand Mar. 19, 1929 1,858,755 Van Wyck May 17, 1932 1,860,685 Morris.- May 31,1932 1,880,230 Beck Oct. 4, 1932 1,906,406l Chromy Apr. 25, 193-3 1,998,429 Andre et al. Apr. 23, 1935 2,046,044 Vissing June 30, 1936 2,038,506 lCadieux Apr. 21,1936 2,068,360v Van Deventer Jan.- 19i 1937 'Ba'rtowfft-r---f-r-f 2,296,936 Logan etalf ,.,.f Sept29i1942, 1". FOREIGN PATENTS Number Country, Date Italyv June'22 1936 

